Most of the time, we as cell phone users have no idea what type of technology the phone is using, and we don't need to know any of this, either. Using a cell phone should be - and is - as simple as using a regular phone.

If simply calling from your phone to someone else, it really makes no difference to you as a user if your phone is using GSM or any other type of wireless technology. However, there is one unique feature of GSM service that makes it very valuable when you're traveling, as well as one other feature that is wonderfully common.

The wonderfully common feature is GSM itself. GSM service is available in more than 205 countries all around the world. It is the international standard, with only a very few countries not having GSM (the most notable of which is Japan).

The unique feature is that GSM service is not tied to your phone. With most phones you are familiar with, the phone is coded in such a way that it will only work with one wireless service provider. If you change wireless service providers, you have to change phones, too.

A GSM cell phone is compatible with any GSM service provider that is running on the same frequency. Your unique account information is instead encoded into a removable chip - what is called a 'SIM' (Subscriber Information Module).

The wonderful convenience of this is that you can simply replace one SIM from one service provider with another SIM from another service provider, and your phone instantly starts working on the new service, and forgets all about being previously connected to the first service. This means you could, if you wished, travel to a dozen different countries, and with a dozen different SIMs, change your phone to work with each different country's phone service as effortlessly as it takes to unplug the chip and replace it with a new one as you cross each border.

This is the real magic of GSM phones. You only need to buy one phone, and then can use as many different SIMs as you need for the countries you're visiting.

Universal compatibility – theory vs reality

In theory, any GSM phone should be capable of working with any GSM service, anywhere in the world.

There are two factors that might prevent this from occurring.

• Wrong frequency
  Your phone must have the same frequency band that the GSM service is being broadcast on to be able to make and receive calls. This is discussed in this article – What sort of international cell phone do you need.
• Locked phone
  If you bought your phone from a regular wireless service provider, they may have locked your phone so it only works with their SIM. You need to be sure that your phone is unlocked and will work with every company's SIM. All the phones we sell are unlocked. If you already have a locked phone, we may be able to unlock it for you – see our article Unlocking your GSM cell phone.